Field of the Invention
This invention relates to optical display technologies, and in particular, it relates to a light source system and projection display device.
Description of Related Art
In conventional light source systems, spatial light modulators (SLMs) are used to perform spatial modulation of light. Single SLM, two-SLM and three-SLM systems have their respective advantages and are used in various projection display devices. The operation principle of single SLM system is: Multiple primary color lights are alternatingly inputted to the SLM to be modulated; the monochromatic images projected on the screen are switched at high frequency, and the monochromatic images in a time sequence are combined into a color image by the effect of persistence of vision of the human eyes. However, due to the limitations in the switching frequency, a “rainbow” effect may exist. Also, the utilization efficiency of the light source is not high, making it difficult to increase the brightness of the light source system employing single SLM. But because of its low cost, single SLM is widely used in low-end projection display devices. The operation principle of three-SLM system is: Three primary color lights are simultaneously inputted to three independent SLMs to be modulated by them respectively. The monochromatic images are combined to generate a color image. Because it does not use a time sequence of monochromatic lights, the “rainbow” effect is effectively eliminated. Also, the light source does not need to be converted or filtered, which improves the utilization efficiency of the light source. However, because of its high cost, it is typically used in high-end projection display devices, such as in cinemas. To overcome the respective shortcomings of single SLM and three-SLM light source systems, two-SLM devices are developed, where one SLM processes one primary color light, and the other SLM processes two other primary color lights. The outputs of the two SLMs overlap in some time intervals (each processing one primary color light respectively), which increases the switching frequency as compared to the single SLM system, but is less costly than three-SLM system because it uses one fewer SLM. Thus, two-SLM systems are the focus of research in the projection display field.
However, two-SLM systems also have problems that need to be solved. For example, in Chinese patent application No. 201210370655.9, described here with reference to FIG. 1, the system includes an excitation light source 1, a color wheel 2, a light separation and combination device 3, a first SLM 4 and a second SLM 5. The color wheel 2 is divided into two segments each provided with a wavelength conversion material. One of the segments is excited by the excitation light source 1 to generate a first converted light, which is separated by the light separation and combination device 3 into two lights which are respectively inputted to the first SLM 4 and the second SLM 5 to be modulated. The other one of the segments is excited by the excitation light source 1 to generate a second converted light, which is directed by the light separation and combination device 3 to be inputted into the second SLM 5 to be modulated. Compared to a single SLM system, this system can increase the brightness and eliminate rainbow effect, and compared to three-SLM system, it can lower the cost. However, this system still has its shortcomings: By using two SLMs to process the three primary color lights, the color gamut of the displayed image is limited, as a result, the images outputted by the light source system to the display screen are not sufficiently realistic. Further, because a single light source is used to generate the converted light to be sequentially inputted to the SLMs, the SLMs are not fully utilized, so the image brightness is still low and cannot meet the requirement of low cost and high quality products.
Therefore, there is a need for a light source system and projection display device which can solve the high cost and low quality problem of conventional light source systems and projection display devices.